回複：印尼奧賽題（1星）

1. 12個奇因子, 36個偶因子. 5^6 – 1 = 2^3 * 3^2 * 7 * 31, so the number of odd divisors is 3*2*2=12(if we consider 1 as a divisor), and the number of even divisors is 3*3*2*2=36(if we consider the number itself as a divisor).

2. 18分鍾

3. 8種換法, we can put – in front of (10,3),(9,4),(8,5),(8,3,2),(7,6),(7,4,2),(6,5,2), (6,4,3).